Method for superplastic forming of rapidly solidified magnesium base metal alloys

Abstract

A complex part composed of rapidly solidified magnesium base metal alloy is produced by superplastic forming at a temperature ranging from 160 DEG C. to 275 DEG C. and at a rate ranging from 0.00021 m/sec to 0.00001 mm/sec, to improve the formability thereof and allow forming to be conducted at lower temperature. The rapidly solidified magnesium based alloy has a composition consisting essentially of the formula MgbalAlaZnbXc, wherein X is at least one element selected from the group consisting of manganese, cerium, neodymium, praseodymium and yttrium, "a" ranges from 0 to about 15 atom percent, "b" ranges from 0 to about 4 atom percent and "c" ranges from about 0.2 to 3 atom percent, the balance being magnesium and incidental impurities, with the proviso that the sum of aluminum and zinc present ranges from about 2 to 15 atom percent. Such an alloy contains fine grain size and finely dispersed magnesium-, aluminum- rare earth intermetallic phases. When formed, the part exhibits good corrosion resistance together with high ultimate tensile strength and good ductility at room temperature, which properties are, in combination, far superior to those of conventional magnesium alloys. The part is suitable for application as a structural member in helicopters, missiles and air frames where good corrosion resistance in combination with high strength and ductility is important.

We claim: 
     
       1. A method of making a superplastic forming form a consolidated metal article, said article having been made by compacting a rapidly solidified magnesium based alloy powder consisting of the formula Mg bal  Al a  Zn b  X c , wherein X is at least one element selected from the group consisting of manganese, cerium, neodymium, praseodymium, and yttrium, "a" ranges from about 0 to 15 atom percent, "b" ranges from about 0 to 5 atom percent, "c" ranges from about 0.2 to 3 atom percent, the balance being magnesium and incidental impurities, with the proviso that the sum of aluminum and zinc present ranges from about 2 to 15 atom percent, said alloy having a microstructure comprised of a substantially uniform cellular network of solid solution phase of a size ranging from 0.2-1.0 micron together with precipitates of magnesium and aluminum containing intermetallic phases of a size less than 0.1 micron, comprising the step of forming said article at a forming rate ranging from about 0.00021 m/sec to 0.00001 m/sec. 
     
     
       2. A method as recited by claim 1, wherein said forming step is carried out at a temperature ranging from about 160° to 275° C. 
     
     
       3. A method as recited by claim 2, wherein said forming step is an extrusion step. 
     
     
       4. A method as recited by claim 2, wherein said forming step is a forging step.